Rodents are mammals and about 40% of mammal species are rodents. They are found in vast numbers on all continents other than Antarctica. Common rodents include mice, rats, squirrels, porcupines, beavers, guinea pigs, and hamsters. Rodents use their sharp incisors to gnaw wood, break into food, and bite predators. Most rodents eat seeds or plants, though some have more varied diets. Some species have historically been pests, eating seeds stored by people and spreading disease.